Method of coating glassine



Patented Nov. 20, 195i METHOD OF COATING GLASSINE Garrett H. Peters,Rhinelander, Wis., assignor to Rhinelander Paper Company,

Rhinelander,

Wis., a corporation of Wisconsin No Drawing. Application November 12,1947, Serial No. 785,521

5 Claims. (Cl. 117-7 6) The present invention relates to a methodofcoating paper, and more particularly, to a method of forming an adherentcoating of a synthetic lacquer on glassine.

Glassine is a relatively transparent, greaseproof paper, formed of wellhydrated cellulosic fibers, that has been s uper-calendered. Sinceglassine paper is inherently brittle, it is customary to plasticizeglassine in order that it may be used satisfactorily in automaticwrapping machines. It has also been customary to coat glassine with waxin order to impart moisture-proofness and heat-sealing propertiesthereto. How ever, wax alone does not give entirely satisfactoryheat-sealing properties.

It has therefore been proposed ,to employ thermoplastic resinsv forheat-sealing purposes. However, due to lack of adhesion between glassine and certain lacquers, for example thermoplastic resins, such asvinyl polymers and various rubber compositions, this proposal has notthus far gone into extensive commercial use. These lacquer films aretooeasily stripped from the glassine base to make satisfactory coatedproducts.

The present invention provides a method whereby an adherent coating ofsynthetic'lacquer may be applied to glassine or similar papers. Theimproved results of the method of the present invention are obtained bya pre-treatment of the glassine with an aqueous solution of a rl b e enils lt. Preferab Salts are employed which may be mixed with theplasticizers for joint application to the web on. the paper machine. Theaqueous solution of the salts and of the plasticizers may suitably beapplied to the web by means of a'size press located between sections ofthe driers. Thus, it is not necessary to "provide a separate dampener orother means for applying the aqueous solution to the paper.Alternatively, prior to the supercalendering step, the machinefinished-greaseproof paper may be passed through a dampener containingan aqueous solution of the salt. The super-calendered and finishedglassine is then passed through suitable coating apparatus, such as aconventional roller coating machine, by

means of whichthe synthetic lacquerniay be use in the process of thepresent invention. The

alkali metal and ammonium salts of such polyprotic acids as carbonicacid, orthophosphoric' acid, pyrophosphoric acid, metasilicic acid,orthosilicic acid and mixtures of silicic acids may be employed in thepresent invention. I have invention, including vinyl resins, such as thecopolymers of vinyl acetate and vinyl chloride, cyclized rubbers, andchlorinated rubbers.

, The coated product obtained by the use of the present invention hasenhanced transparency in comparison with glassine itself, and the addedadvantages of high moisture resistance, of ability to heat seal atrelatively low temperature's, and of improved flexibility. Thesedesirable characteristics are obtained along with a strong adherence ofthe coating film to the glassine base.

It is, therefore, an important object of the present invention toprovide a method for coating glassine with a resinous lacquercomposition .to form an adherent film of the lacquer on the surface ofthe glassine.

It is a further important object of the present invention to provide amethod of pre-treating glassine so that a resinous lacquer compositionsubsequently applied to the glassine surface will be strongly adherentthereto.

It is a still further object of the present invention to provide amethod of coating glassine with a resinous lacquer which comprisespre-treating the glassine with an aqueous solution of an alkali metal orammonium salt of a polyvalent and slightly ionized inorganic acid.

It is a yet further object of the present invention to provide a methodfor the preparation of coated glassine which comprises treating thesurface of the glassine with an aqueous solution of a compound selectedfrom the group consisting of alkali metal and ammonium carbonates,silicates and phosphates, and thereafter applying a syntheticthermoplastic lacquer composition to the treated surface of theglassine.

Other and further important objects of this invention Will becomeapparent from the following description and appended claims.

As has been hereinbefore stated, the aqueous salt solution of thepresent invention comprises an aqueous solution of an alkali metal orammonium salt of a polyvalent, slightly ionized in-.- organic acid. Ihave found that the alkali metal and ammonium salts of such polyproticacids as carbonic acid, phosphoric acid, pyrophosphoric acid,metasilicic acid and orthosilicic acid are suitable salts for'use in thepresent invention. I have found that the sodium and potassiumcarbonates, phosphates and silicates and ammonium secondary phosphateare particularly desirable salts for such use.

The concentration of the salt solution is dependent upon the solubilityof the salt in water at the temperature employed. I have found that maybe employed in the process of the present solutions which are ofsufficient concentration to deposit from 1 to 5% of the salt based onthe air-dry weight of the fiber in the paper are operative to give theimproved results of the pres.

ent invention. of'course, more concentrated solutions ma be employed,but since a larger amount is not necessary, it would not be commerciallydesirable to employ amounts in excess of about by weight.

The thermoplastic resins which may be deposited on a treated glassine inaccordance with the method of the present invention are prererablyresinous lacquers which foiin a trans parent, adherent film on thetreated glass'ine surface. I have found various resinous lacquers,

including copolymers of vinyl chloride and vinyl acetate, chlorinatedrubbers, and cycle-rubbers may be employed. These lacquers are suitablenot only because of the excellent physical propcities and chemicalresistance of the composi tions, but also for the heat-sealingproperties of the lacquers.

as has been hereinbefore stated, the salt *solution may be applied tothe web on the paper machine in intimate mixture with the plasticizeremployed in the preparation of the glassine, or. alternatively, the saltsolution may be applied to the paper by a size press prior to the supercalendering operation. It is preferred that the aqueous salt solution beapplied to the web in mixture with the plasticizers, since this methodeliminates the necessity of a separate dampening bath or other apparatusfor use in the applica tion of the salt solution to the paper. A

The resinous lacquer may be applied to the treated glassine by anysuitable method. It is preferred that the application or the lacquer becarried out in a coating apparatus such as j a conventionaldouble-roller coating machine, By the use of such a "double-rollercoating machine, both sides of the glassine may be simultaneously coatedwith the resinous lacquer. Following the application of the resinuouslacquer as a solution to the treated surfaces, the wet'g1assine isheated, as by passing the "coated product through a dry tunnel, to e'aporateth'e solvents from the lacquer and also to effect curing er thecoated fiiei j warrant-11mins my intention to any'p'artiou raiproeeutie,the ronowingexampie, in writer; 1) by weight are given, will serve toillustrate nemesis its preferred form.

EXAMPLE Glassine wascoated in accordance with the present invention asfollows: v "The paper was made from wood pulp pn a Fourdrinier papermaking machine. A The web on the machine was passed through atankcont'aifiiii .pl'asticiz'er and an aqueous solution or a his suitablesalt as hereinbefore described. The treated paperis thensupeif-ealehdered by contensor-m methods used iii the manufacture ofglassine. The glassine thus prepared was then passed through the rollersof a double-roller coating machine having horizontal parallel rollsplaced one above the other. The bottom roll ran ina sexier lacquerfandcoated the lower surface pr eg aisfsirie. fI'he upper surface of theglassine is coated by lacquer pumped from the lower lacquer pan andsprayed on the upper surface ahead of the upper roll. Any excess lacquerwas removed from the coated glassine by the squeezing action of therolis. The wet coated glassine is then passed to adrying tunnelmaintained at a temperature of 150" to 200 F. to evaporate solvent fromthe lacquer.

The results obtained froinjth e use of a "ra es sentative groupof salts,selected from the alkali metal and ammonium phosphates, carbonates andsilicates, in combination with two types of suitable resinous lacquersare tabulated in the following tables. The physical-properties of thecoated l'as'sine's were determined on coated p i d ucts 'obtained by theuse of a salt concentration which was suflicient tocep s t 1, 2-, and 5%r salt based on the weight of fiber ifl jth'e paper. Each of the threeconcentrations has been found satisfactory, notes/ea r clarity and'br'iefness onlythose results obtained at a concentration of 5%arepresentetl W T H The resino s lacquer amt-demons em' iayed are asfollows:

Copolymer of vinyl acetate, vinyl chloride, and maleic anli ydndea ascizer. forflcopq ymer utylpht alyl butyl .glycolate,GifltOCOCtHiCOOCHiCOOGiHV).

Methylethyl ketone.

Toluene.

Number it re t; Weight Goin-ponant eyelashes Psi-emu Toluene.

. (M. r. 13s-14o it). 400. 0

. I th fo owi elesfih i w es 'm si have the indicated significance:Ex-excel1ent, G-good-, F-fair.

ti its has at a l y a a t, No. Salt Tots? sol) Lacquer Sim pawn? ColorGloss Retained 860 I it '3 5 x l. TI .6

5 7.31 1 Ex 72 F F 5 6.80 I E: 78 'G G a i 11 -EX I u w -5 5,21 1 o 74 r,r

-5 9.27 "1 Ex 59 F F 8' Nz'uSiO'i 5 8.61 .-I Ex 53 F F U V II E; a 9-"-NazSiO; '5 8.44 I EX F G I II F It will, of course, be understood thatvarious details of the process may be varied through a wide rangeWithout departing from the principles of this invention, and it is,therefore, not the purpose to limit the patent granted hereon otherwisethan necessitated by the scope of the appended claims.

I claim as my invention:

1. A method of coating glassine which comprises treating glassine stockin web form with an aqueous solution consisting essentially of a saltselected from the group consisting of alkali metal and ammoniumphosphates, silicates and carbonates, drying the thus treated glassinestock and applying to said treated surface a resinous lacquer in whichthe resinous constituent consists of a thermoplastic resin selected fromthe group consisting of cyclized rubbers, chlorinated rubbers, and avinyl co-polymer consisting of vinyl chloride and vinyl acetate, whichresinous constituents do not adhere well to glassine when not sotreated.

2. In a method of coating glassine with a resinous lacquer compositioncontaining paraffin wax and in which the resinous constituent consistsof a thermoplastic resin selected from the group consisting of cyclizedrubbers, chlorinated rubbers, and a vinyl copolymer consisting of vinylchloride and vinyl acetate, which lacquer compositions do not adherewell to glassine, the improvement which comprises treating the glassinestock in web form with an aqueous solution consisting essentially of asalt selected from the group consisting of alkali metal and ammoniumphosphates, silicates and carbonates, and supercalendering and dryingthe thus treated glassine stock prior to the application to said treatedglassine stock of said resinous lacquer composition, whereby theadhesion of said resinous lacquer composition to said surface isimproved.

3. In a method of making a coated glassine including the steps ofsupercalendering a dampened web of well hydrated cellulosic fibers, theimprovement which comprises treating said Well hydrated cellulose fibersin Web form with an aqueous dampening solution of a salt selected fromthe group consisting of alkali metal and ammonium phosphates, carbonatesand silicates, supercalendering the thus treated web to thereby dry andfinish the same and applying thereto a resinous lacquer in which theresinous constituent consists of a thermoplastic resin selected from thegroup consisting of cyclized rubbers, chlorinated rubbers, and a vinylco-polymer consisting of vinyl chloride and vinyl acetate, whichresinous constituents normally do not adhere well to untreated glassine,whereby the adherence of the resinous constituent, so selected isimproved.

4. In a method of coating glassine with a resinous lacquer compositionin which the resinous constituent consists of a vinyl co-polymerconsisting of vinyl chloride and vinyl acetate that does not adhere wellto an untreated glassine, the improvement which comprises treatingglassine stock in web form with an aqueous solution consistingessentially of a salt selected from the group consisting of alkali metaland ammonium phosphates, silicates and carbonates, drying the thustreated glassine stock and thereafter applying to said treated surfacesaid vinyl copolymer, the treatment with said aqueous solution servingto improve the adherence of said vinyl co-polymer to the glassine stock.

5. In a method of coating glassine with a vinyl co-polymer consisting ofvinyl chloride and vinyl acetate, which co-polymer normally does notadhere well to glassine, the improvement which comprises first treatingglassine stock in web form with an aqueous solution consistingessentially of a salt selected from the group consisting of alkali metaland ammonium phosphates, silicates and carbonates, drying the thustreated glassine stock and subsequently applying to said treated surfacesaid vinyl co-polymer consisting of vinyl chloride and vinyl acetate asaforesaid, the treatment of said glassine with said aqueous saltsolution serving to improve the adherence of said copolymer to saidglassine stock.

GARRETT H. PETERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 524,024 Howe Aug. 7, 18941,597,840 Summers Aug. 31, 1926 2,058,961 Dozier Oct. 27, 1936 2,163,085Cupery June 20, 1939 2,244,795 Williams June 10, 1941 2,268,674 RothJan. 6, 1942 2,291,616 Fletcher Aug. 4, 1942 2,300,373 Stoner et al.Oct. 27, 1942 2,333,023 Manor Oct. 26, 1943 2,403,697 Wenberg July 9,1946

